Interfacial catalysis: the mechanism of phospholipase A2.
A chemical description of the action of phospholipase A2 (PLA2) can now be inferred with confidence from three high-resolution x-ray crystal structures. The first is the structure of the PLA2 from the venom of the Chinese cobra (Naja naja atra) in a complex with a phosphonate transition-state analogue. This enzyme is typical of a large, well-studied homologous family of PLA2S. The second is a similar complex with the evolutionarily distant bee-venom PLA2. The third structure is the uninhibited PLA2 from Chinese cobra venom. Despite the different molecular architectures of the cobra and bee-venom PLA2s, the transition-state analogue interacts in a nearly identical way with the catalytic machinery of both enzymes. The disposition of the fatty-acid side chains suggests a common access route of the substrate from its position in the lipid aggregate to its productive interaction with the active site. Comparison of the cobra-venom complex with the uninhibited enzyme indicates that optimal binding and catalysis at the lipid-water interface is due to facilitated substrate diffusion from the interfacial binding surface to the catalytic site rather than an allosteric change in the enzyme's structure. However, a second bound calcium ion changes its position upon the binding of the transition-state analogue, suggesting a mechanism for augmenting the critical electrophile.
Scott
D L
DL
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511.
White
S P
SP
Otwinowski
Z
Z
Yuan
W
W
Gelb
M H
MH
Sigler
P B
PB
D001514:Bee Venoms / Q000032:analysis; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002384:Catalysis; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004546:Elapid Venoms / Q000032:analysis; D008958:Models, Molecular; D015394:Molecular Structure; D063065:Organophosphonates / Q000378:metabolism; D010741:Phospholipases A / Q000737:chemistry / Q000378:metabolism*; D054467:Phospholipases A2; D010743:Phospholipids / Q000378:metabolism; D011487:Protein Conformation; D014961:X-Ray Diffraction
D001514:Bee Venoms; D004546:Elapid Venoms; D063065:Organophosphonates; D010743:Phospholipids; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium